1. Field of the Invention:
This invention relates to cameras having electric motors for film transportation.
2. Description of the Prior Art:
Currently, the rewinding of the film in a camera has been performed by engaging a rewind member on the camera housing with the spool of the film cartridge. Because the size of the cartridge varies from film type to type, however, a so-called "jiggling" takes place during the rewinding operation. It has, therefore, been difficult to transmit the driving torque to the spool with good efficiency. Even if the casing of the cartridge is held stationary in the chamber therefor, because the spool itself is very loosely mounted in the cartridge casing, a similar problem will arise. Further, to facilitate a smooth coupling of the rewind member into the recess of the spool of the cartridge, the rewind member must be formed to enable a large play in the spool recess. With the addition of this condition, the difficulty of achieving a driving torque transmission with good efficiency is intensified. Thus, the power necessary to perform all rewinding has been very large.
Such waste of energy, though negligible in the case of manual rewinding, leads, in the case of motorized rewinding, to a premature consumption of the battery, and another difficult problem of assuring the maximum torque to the film rewinding under the worst conditions.
In the art of motor built-in single lens reflex cameras, the film transportation and the charging of the internal mechanisms have generally been carried out by only one electric motor. It is to be noted here that when in the winding mode, the film is driven to move by a sprocket for the purpose of accurately adjusting the shift of the film to one frame. The use of one motor, however, gives rise to the following problems:
(i) The two requirements of assuring a sufficient film transporting power and of insuring that damage of the perforations of the film are avoided are difficult to fulfill simultaneously.
(ii) Because, during winding, friction is used in driving the take-up spool, the energy loss due to slippage is large.
(iii) Because the supply and take-up spools are located at either end of the lateral length of the camera, the use of only one motor makes it difficult to achieve a good efficiency of power transmission in both directions to the supply and take-up spools.
For the leaf shutter types of cameras of which the load on charging is small, the above-described problems have been overcome by various proposals. But, it is difficult to apply such a proposal without any alteration to lens-interchangeable single lens reflex cameras of which the load on charging of the lens and shutter is very large.
So, in the single lens reflex camera, besides the motor for film transportation, an additional motor may be considered to be used exclusively for charging the shutter and the lens as is known in the proposal of U.S. Pat. No. 4,204,759. In this proposal, however, the latter motor is put in a space near the bottom of the mirror box. But, this space is usually occupied by the focus detecting mechanism when the automatic focusing function is imparted to the camera.
To avoid this problem, the second motor may be positioned adjacent to the cartridge chamber to be used not only for rewinding but also for driving the auto-focus (hereinafter abbreviated as "AF") mechanism as is known in the proposal of U.S. Pat. No. 4,405,221. In this proposal, however, the selective transmission of the driving torque of the motor to the AF driving system and the rewinding system must be controlled manually, giving rise to a problem when it is desired to achieve an improvement in automation of the camera.
Concerning the auto loading of film, the prior known method utilizes friction in rotating the spool to take up the film. Recently, to avoid the energy loss due to the friction, another method of directly driving the spool has found increasing use in the cameras. The cameras employing the latter method involve an inconvenience in that the photographer must take sure the film leader is pulled out to, and then accepted by, the take-up spool, or otherwise the automatic film loading mechanism would not work. So, an attempt has been made to provide for the sprocket with a one-way clutch arranged to allow the sprocket to move the film until the film engages with the spool, and after that, the spool to wind up the film. Since, at the early stage of the loading operation, however, this method brings only one side of the width of the film into engagement with the sprocket at the perforations thereof, there exists some possibility of damaging the perforations before the film leader reaches the take-up spool. If so, the automatic loading will fail.
To eliminate such problem, another sprocket may be additionally used as arranged near the cartridge chamber to engage the perforations of the upper and lower edges of the film at a time. With the use of one motor in driving the two sprockets, however, when such method is applied to the single lens reflex camera, as the upper and lower spaces on either side of the exposure aperture between the two sprockets are occupied by the penta prism and the mirror box with the focus detecting device respectively, the following problem is produced: That is, because of the necessity of creating a space which the required driving torque transmission occupies either above the penta prism, or below the focus detecting device, a large increase in the size of the camera is called for. Also, as the length of the path of transmission increases, the efficiency of driving torque transmission rapidly lowers, leading to a waste of electrical energy.
A motor for driving of the automatic focusing lens and an electrical power source therefor have been put within the lens mounting unit. Such arrangement was, however, objectionably incompatible with the compact design of objectives having the automatic focusing function. With respect to the electrical power source, the problem can be solved when an electrical interconnection is used to permit the common use of the battery within the camera housing. To remove the motor for driving the automatic focusing lens also it may be considered to commonly use the otherwise driving purpose motor. But, for the automatic focusing lens too, there is need to provide two way, or forward-reversed, driving. In order to properly perform these aspects of driving, a simple planetary gear could not suffice for the direction changeover mechanism.
Recently, as the automation of cameras is advancing, an automatic rewinding system also has been developed that when the film has all been exposed as detected by some means, the film starts to be rewound automatically. In the camera of this kind, as only one motor is used, the revolution of the planetary gear is utilized to convert the direction of rotation of the motor, thereby it being made possible to selectively operate the winding and rewinding modes.
To assure a precise interval between successive picture frames, however, a winding stop member for controlling the advancement of the film in each cycle of film winding operation becomes necessary. When in the rewinding mode, this winding stop member must be released. For this purpose, an electromagnet may be used. But because it consumes electrical energy during rewinding, this method is not preferred.